The present invention relates to a code wheel for use in a reflective optical rotary encoder, and more particularly to a code wheel for a reflective optical rotary encoder which detects the speed and direction of rotation of the code wheel by radiating light onto a pattern of reflecting and non-reflecting areas on the code wheel and receiving reflected light from the code wheel.
Conventional rotary encoder code wheels will be described with reference to FIGS. 1 through 3 of the accompanying drawings.
As shown in FIG. 1, a disk-shaped code wheel 2 is mounted on a shaft 1a of a motor 1 and has a flat upper surface 2a having thereon a plurality of radial, substantially sectorial reflecting areas 3 spaced at equal angular intervals and a plurality of radial non-reflecting areas 4 between the reflecting areas 3. A single light-emitting element 5 and two photodetectors 6, 7 one on each side of the light-emitting element 5 are disposed in confronting relation to the upper surface 2a with optical fibers 8, 9, 10 interposed. When the code wheel 2 is rotated, a beam of light emitted from the light-emitting element 5 is reflected by the reflecting areas 3 and detected by the two photodetectors 6, 7 as successive pulse signals, which are processed to determine the speed and direction of rotation of the code wheel 2.
FIGS. 2A and 2B show a conventional code wheel for use in the above encoder. The code wheel, designated at 2, is of a disk shape made of a non-reflecting material as shown in FIG. 2A. On the flat upper surface 2a of the code wheel 2, there are deposited radial sectorial reflecting layers 3 by hot stamping or vapor deposition as shown in FIG. 2B, leaving portions of the upper surface 2a between the adjacent reflecting members 3 as non-reflecting areas 4.
With the conventional code wheel as shown in FIGS. 2A and 2B, it is relatively expensive to form the reflecting layers 3, and the code wheel does not lend itself to mass production and hence cannot be lowered in cost.
FIG. 3 illustrates another conventional code wheel. The disk-shaped code wheel, denoted at 11, is formed of a reflecting material and has an upper surface 11a to which is applied a mask 12 of a non-reflecting material having radial sectorial slits 12a defined therein. Portions of an upper surface 11a of the code wheel are utilized as reflecting areas, while the mask 12 itself serves as non-reflecting areas.
The slits 12a in the mask 12 are normally punched or etched, a process which results in a poor parting accuracy of the edges of the slits 12a which define the reflecting and non-reflecting areas. The code wheel of FIG. 3 is therefore unable to increase the resolution of an encoder for detecting optical pulses.